467 research outputs found
Is there a hidden hole in Type Ia supernova remnants?
In this paper we report on the bulk features of the hole carved by the
companion star in the material ejected during a Type Ia supernova explosion. In
particular we are interested in the long term evolution of the hole as well as
in its fingerprint in the geometry of the supernova remnant after several
centuries of evolution, which is a hot topic in current Type Iasupernovae
studies. We use an axisymmetric smoothed particle hydrodynamics code to
characterize the geometric properties of the supernova remnant resulting from
the interaction of this ejected material with the ambient medium. Our aim is to
use supernova remnant observations to constrain the single degenerate scenario
for Type Ia supernova progenitors. Our simulations show that the hole will
remain open during centuries, although its partial or total closure at later
times due to hydrodynamic instabilities is not excluded. Close to the edge of
the hole, the Rayleigh-Taylor instability grows faster, leading to plumes that
approach the edge of the forward shock. We also discuss other geometrical
properties of the simulations, like the evolution of the contact discontinuity.Comment: 48 pages, 17 figures; Accepted for publication in Ap
Thermal X-Ray Emission from Shocked Ejecta in Type Ia Supernova Remnants II: Parameters Affecting the Spectrum
The supernova remnants left behind by Type Ia supernovae provide an excellent
opportunity for the study of these enigmatic objects. In a previous work, we
showed that it is possible to use the X-ray spectra of young Type Ia supernova
remnants to explore the physics of Type Ia supernovae and identify the relevant
mechanism underlying these explosions. Our simulation technique is based on
hydrodynamic and nonequilibrium ionization calculations of the interaction of a
grid of Type Ia explosion models with the surrounding ambient medium, coupled
to an X-ray spectral code. In this work we explore the influence of two key
parameters on the shape of the X-ray spectrum of the ejecta: the density of the
ambient medium around the supernova progenitor and the efficiency of
collisionless electron heating at the reverse shock. We also discuss the
performance of recent 3D simulations of Type Ia SN explosions in the context of
the X-ray spectra of young SNRs. We find a better agreement with the
observations for Type Ia supernova models with stratified ejecta than for 3D
deflagration models with well mixed ejecta. We conclude that our grid of Type
Ia supernova remnant models can improve our understanding of these objects and
their relationship to the supernovae that originated them.Comment: Accepted for publication in Ap
An Emerging Class of Bright, Fast-evolving Supernovae with Low-mass Ejecta
A recent analysis of supernova (SN) 2002bj revealed that it was an apparently
unique type Ib SN. It showed a high peak luminosity, with absolute magnitude
M_R -18.5, but an extremely fast-evolving light curve. It had a rise time of <7
days followed by a decline of 0.25 mag per day in B-band, and showed evidence
for very low mass of ejecta (<0.15 M_Sun). Here we discuss two additional
historical events, SN 1885A and SN 1939B, showing similarly fast light curves
and low ejected masses. We discuss the low mass of ejecta inferred from our
analysis of the SN 1885A remnant in M31, and present for the first time the
spectrum of SN 1939B. The old environments of both SN 1885A (in the bulge of
M31) and SN 1939B (in an elliptical galaxy with no traces of star formation
activity), strongly support old white dwarf progenitors for these SNe. We find
no clear evidence for helium in the spectrum of SN 1939B, as might be expected
from a helium-shell detonation on a white dwarf, suggested to be the origin of
SN 2002bj. Finally, the discovery of all the observed fast-evolving SNe in
nearby galaxies suggests that the rate of these peculiar SNe is at least 1-2 %
of all SNe.Comment: Additional analysis included. ApJ, in pres
Intraspecific and interstage similarities in host-plant preference in the diamondback moth (Lepidoptera: Plutellidae)
The diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), is an important insect pest of cruciferous crops. Understanding its preference patterns can lead to more efficient management methods, such as trap crops. Several strains of P. xylostella were used to test whether there were differences in oviposition preference in a four-choice setting, on abaxial versus adaxial leaf surfaces in 28 different plant species, and on substrates with different concentrations of sinigrin (allylglucosinolate). Additionally, the larval preference of P. xylostella was studied with 17 plant species of known glucosinolate content that were compared to Arabidopsis thaliana L. in two-choice tests. Our research shows that the diet on which P. xylostella has fed hardly affects multiple-choice host-plant preference, abaxial and adaxial oviposition preference, or oviposition response to pure glucosinolates. Our study also shows that glucosinolate content affects larval preference, which together with the known correlation between glucosinolate content and P. xylostella oviposition, indicates that crops with high glucosinolate content could be more susceptible to damage by P. xylostella than crops with low glucosinolate content. These findings are discussed in regards to their significance in the management of P. xylostella
Typing Supernova Remnants Using X-ray Line Emission Morphologies
We present a new observational method to type the explosions of young
supernova remnants (SNRs). By measuring the morphology of the Chandra X-ray
line emission in seventeen Galactic and Large Magellanic Cloud SNRs with a
multipole expansion analysis (using power ratios), we find that the
core-collapse SNRs are statistically more asymmetric than the Type Ia SNRs. We
show that the two classes of supernovae can be separated naturally using this
technique because X-ray line morphologies reflect the distinct explosion
mechanisms and structure of the circumstellar material. These findings are
consistent with recent spectropolarimetry results showing that core-collapse
SNe are intrinsically more asymmetric.Comment: 4 pages, 1 figure, accepted for publication in ApJ
Thermonuclear supernova models, and observations of Type Ia supernovae
In this paper, we review the present state of theoretical models of
thermonuclear supernovae, and compare their predicitions with the constraints
derived from observations of Type Ia supernovae. The diversity of explosion
mechanisms usually found in one-dimensional simulations is a direct consequence
of the impossibility to resolve the flame structure under the assumption of
spherical symmetry. Spherically symmetric models have been successful in
explaining many of the observational features of Type Ia supernovae, but they
rely on two kinds of empirical models: one that describes the behaviour of the
flame on the scales unresolved by the code, and another that takes account of
the evolution of the flame shape. In contrast, three-dimensional simulations
are able to compute the flame shape in a self-consistent way, but they still
need a model for the propagation of the flame in the scales unresolved by the
code. Furthermore, in three dimensions the number of degrees of freedom of the
initial configuration of the white dwarf at runaway is much larger than in one
dimension. Recent simulations have shown that the sensitivity of the explosion
output to the initial conditions can be extremely large. New paradigms of
thermonuclear supernovae have emerged from this situation, as the Pulsating
Reverse Detonation. The resolution of all these issues must rely on the
predictions of observational properties of the models, and their comparison
with current Type Ia supernova data, including X-ray spectra of Type Ia
supernova remnants.Comment: Invited talk at the Conference on Interacting Binaries: Accretion,
Evolution and Outcomes, Cefalu, Italy, July 2004, 10 pages, LaTeX, 3 eps
figure
The kinematics and chemical stratification of the Type Ia supernova remnant 0519-69.0
We present an analysis of the XMM-Newton and Chandra X-ray data of the young
Type Ia supernova remnant 0519-69.0 in the Large Magellanic Cloud. We used data
from both the Chandra ACIS and XMM-Newton EPIC-MOS instruments, and high
resolution X-ray spectra obtained with the XMM-Newton Reflection Grating
Spectrometer. The Chandra data show that there is a radial stratification of
oxygen, intermediate mass elements and iron, with the emission from more
massive elements more toward the center. Using a deprojection technique we
measure a forward shock radius of 4.0(3) pc and a reverse shock radius of
2.7(4) pc. We took the observed stratification of the shocked ejecta into
account in the modeling of the X-ray spectra with multi-component NEI models,
with the components corresponding to layers dominated by one or two elements.
An additional component was added in order to represent the ISM, which mostly
contributed to the continuum emission. This model fits the data well, and was
also employed to characterize the spectra of distinct regions extracted from
the Chandra data. From our spectral analysis we find that the fractional masses
of shocked ejecta for the most abundant elements are: M(O)=32%, M(Si/S)=7%/5%,
M(Ar+Ca)=1%, and M(Fe) = 55%. From the continuum component we derive a
circumstellar density of nH= 2.4(2)/cm^3. This density, together with the
measurements of the forward and reverse shock radii suggest an age of 450+/-200
yr,somewhat lower than, but consistent with the estimate based on the optical
light echo (600+/-200 yr). From the RGS spectra we measured a Doppler
broadening of sigma=1873+/-50 km/s, from implying a forward shock velocity of
vS = 2770+/-500 km/s. We discuss the results in the context of single
degenerate explosion models, using semi-analytical and numerical modeling, and
compare the characteristics of 0519-69.0 with those of other Type Ia supernova
remnants.Comment: Astronomy and Astrophysics in press. This version is the A&A accepted
version, which contains improved figures and an extended discussion sectio
A new and unusual LBV-like outburst from a Wolf–Rayet star in the outskirts of M33
MCA-1B (also called UIT003) is a luminous hot star in the western outskirts of M33, classified over 20 yr ago with a spectral type of Ofpe/WN9 and identified then as a candidate luminous blue variable (LBV). Palomar Transient Factory data reveal that this star brightened in 2010, with a light curve resembling that of the classic LBV star AF And in M31. Other Ofpe/WN9 stars have erupted as LBVs, but MCA-1B was unusual because it remained hot. It showed a WN-type spectrum throughout its eruption, whereas LBVs usually get much cooler. MCA-1B showed an almost four-fold increase in bolometric luminosity and a doubling of its radius, but its temperature stayed ≳29 kK. As it faded, it shifted to even hotter temperatures, exhibiting a WN7/WN8-type spectrum, and doubling its wind speed. MCA-1B is reminiscent of some supernova impostors, and its location resembles the isolated environment of SN 2009ip. It is most similar to HD 5980 (in the Small Magellanic Cloud) and GR 290 (also in M33). Whereas these two LBVs exhibited B-type spectra in eruption, MCA-1B is the first clear case where a Wolf–Rayet (WR) spectrum persisted at all times. Together, MCA-1B, HD 5980, and GR 290 constitute a class of WN-type LBVs, distinct from S Doradus LBVs. They are most interesting in the context of LBVs at low metallicity, a possible post-LBV/WR transition in binaries, and as likely Type Ibn supernova progenitors
Ventilatory settings in the initial 72 h and their association with outcome in out-of-hospital cardiac arrest patients: a preplanned secondary analysis of the targeted hypothermia versus targeted normothermia after out-of-hospital cardiac arrest (TTM2) trial
Purpose: The optimal ventilatory settings in patients after cardiac arrest and their association with outcome remain unclear. The aim of this study was to describe the ventilatory settings applied in the first 72 h of mechanical ventilation in patients after out-of-hospital cardiac arrest and their association with 6-month outcomes.
Methods: Preplanned sub-analysis of the Target Temperature Management-2 trial. Clinical outcomes were mortality and functional status (assessed by the Modified Rankin Scale) 6 months after randomization.
Results: A total of 1848 patients were included (mean age 64 [Standard Deviation, SD = 14] years). At 6 months, 950 (51%) patients were alive and 898 (49%) were dead. Median tidal volume (VT) was 7 (Interquartile range, IQR = 6.2-8.5) mL per Predicted Body Weight (PBW), positive end expiratory pressure (PEEP) was 7 (IQR = 5-9) cmH20, plateau pressure was 20 cmH20 (IQR = 17-23), driving pressure was 12 cmH20 (IQR = 10-15), mechanical power 16.2 J/min (IQR = 12.1-21.8), ventilatory ratio was 1.27 (IQR = 1.04-1.6), and respiratory rate was 17 breaths/minute (IQR = 14-20). Median partial pressure of oxygen was 87 mmHg (IQR = 75-105), and partial pressure of carbon dioxide was 40.5 mmHg (IQR = 36-45.7). Respiratory rate, driving pressure, and mechanical power were independently associated with 6-month mortality (omnibus p-values for their non-linear trajectories: p < 0.0001, p = 0.026, and p = 0.029, respectively). Respiratory rate and driving pressure were also independently associated with poor neurological outcome (odds ratio, OR = 1.035, 95% confidence interval, CI = 1.003-1.068, p = 0.030, and OR = 1.005, 95% CI = 1.001-1.036, p = 0.048). A composite formula calculated as [(4*driving pressure) + respiratory rate] was independently associated with mortality and poor neurological outcome.
Conclusions: Protective ventilation strategies are commonly applied in patients after cardiac arrest. Ventilator settings in the first 72 h after hospital admission, in particular driving pressure and respiratory rate, may influence 6-month outcomes
Supernova Remnants as Clues to Their Progenitors
Supernovae shape the interstellar medium, chemically enrich their host
galaxies, and generate powerful interstellar shocks that drive future
generations of star formation. The shock produced by a supernova event acts as
a type of time machine, probing the mass loss history of the progenitor system
back to ages of 10 000 years before the explosion, whereas supernova
remnants probe a much earlier stage of stellar evolution, interacting with
material expelled during the progenitor's much earlier evolution. In this
chapter we will review how observations of supernova remnants allow us to infer
fundamental properties of the progenitor system. We will provide detailed
examples of how bulk characteristics of a remnant, such as its chemical
composition and dynamics, allow us to infer properties of the progenitor
evolution. In the latter half of this chapter, we will show how this exercise
may be extended from individual objects to SNR as classes of objects, and how
there are clear bifurcations in the dynamics and spectral characteristics of
core collapse and thermonuclear supernova remnants. We will finish the chapter
by touching on recent advances in the modeling of massive stars, and the
implications for observable properties of supernovae and their remnants.Comment: A chapter in "Handbook of Supernovae" edited by Athem W. Alsabti and
Paul Murdin (18 pages, 6 figures
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